docs: def cache_control(self):
          """The Cache-Control general-header field is used to specify
          directives that MUST be obeyed by all caching mechanisms along the
          request/response chain.
          """
          def on_update(cache_control):
              if not cache_control and 'cache-control' in self.headers:
                  del self.headers['cache-control']
              elif cache_control:
                  self.headers['Cache-Control'] = cache_control.to_header()
          return parse_cache_control_header(self.headers.get('cache-control'),
                                            on_update,
                                            ResponseCacheControl)